In a spread spectrum communication system, a modulation technique is utilized in which a transmitted signal is spread over a wide frequency band within the communication channel in order to increase the number of simultaneous users in a communication channel without decreasing performance. The baseband signal (e.g., a voice signal with a bandwidth of only a few kilohertz) will be transformed into a signal which occupies and is transmitted over a frequency band that may be many megahertz wide. This is accomplished by spreading the signal to be transmitted with a spreading code. These spreading codes include, but are not limited to, pseudonoise (PN) codes and Walsh codes. A Walsh code corresponds to a single row or column of the Hadamard matrix. For example, a dimension 64 channel Hadamard matrix yields 64 mutually orthogonal Walsh codes. A typical spread spectrum transmission includes a transmitter for expanding the bandwidth of an information signal and transmitting the expanded signal and a receiver for recovering the desired information signal by remapping the received spread spectrum into the original information signal's bandwidth.
The receiver in the spread spectrum communication system will generally include a method to demodulate the transmitted signal and a method to decode the demodulated signal. An optimal decoding metric can be computed but is undesirable because of its complexity. The performance of the previous decoding methods is significantly worse than that of the optimal metric, and previous decoding methods require knowledge of the fading statistics of the channel.
Accordingly, there is a need for a method, decoder circuit, and system for decoding a non-coherently demodulated signal, wherein the method, decoder circuit, and system are less complex than the optimal method, yield better performance than previous methods, and are independent of the fading statistics of the channel.